1. Field of the Invention
The invention relates to a record carrier comprising a servo track indicating an information track intended for recording information blocks represented by marks, said servo track having a periodic variation of a physical parameter at a predetermined frequency and modulated parts for encoding position information at regular intervals, a first type of modulated parts starting with a bit sync element and being of a data type having a data bit element, and a second type of modulated parts starting with a bit sync element and being of a word sync type having a word sync element, the word sync element and the data bit element being modulated according to a same predetermined type of modulation of the periodic variation.
The invention further relates to a recording and/or playback device comprising means for writing and/or reading information blocks in an information track on a record carrier having a servo track indicating the information track, said device comprising means for scanning the servo track and demodulation means for retrieving position information from a signal generated by a variation of a physical parameter of the servo track at a predetermined frequency, said servo track having modulated parts for encoding position information at regular intervals, a first type of modulated parts starting with a bit sync element and being of a data type having a data bit element, and a second type of modulated parts starting with a bit sync element and being of a word sync type having a word sync element, the word sync element and the data bit element being modulated according to a same predetermined type of modulation of the periodic variation.
The invention further relates to a method for manufacturing the record carrier.
2. Description of the Related Art
A record carrier and device for reading and/or writing information are known from International Patent Application No. WO 00/43996, corresponding to U.S. Pat. Nos. 6,538,982 and 6,765,861 (PHN 17323). The information to be recorded is encoded into an information signal which includes address codes and is subdivided in accordance with the address codes into information blocks. The record carrier is of a recordable type and has a servo track, usually called pre-groove, for causing servo signals to be generated when scanning the track. A physical parameter, e.g., the radial position, of the pre-groove periodically varies at a predetermined frequency constituting a so-called wobble. During the scanning of the track, this wobble leads to a variation of the radial tracking servo signals and a wobble signal can be generated. The wobble is modulated according to a type of modulation using phase modulation for encoding position information. The phase modulation or frequency modulation used for encoding digital position information is selected to minimally disturb the component of the predetermined frequency in the wobble signal, because that component is used to control the recording speed. Hence, a majority of the periodic variations needs to be non-modulated, i.e., having the zero crossings not shifted from the nominal positions. During recording, the position information is retrieved from the wobble signal and is used for positioning the information blocks by keeping a predefined relation between the address codes in the information blocks and the position information. The addresses are encoded in modulated parts of the wobble starting with a bit sync element followed by either a word sync element or a data bit element.
A problem of the known system is that detection of the word sync element is not reliable.